The present invention relates to a seal structure for sealing a rotary shaft movable in the axial direction.
A rotary shaft rotated by motive power is utilized in many fields. In agitating devices, a rotary shaft is utilized to rotate an agitating blade to stir an object. Some agitating devices use a rotary shaft movable in the axial direction in order to change the position of the stirring action, which can increase the efficiency of the stirring action.
For sealing such an axially movable shaft, gland packing or segment seals, which permit the movement of the shaft in the axial direction, are exclusively utilized.
Since gland packings or segment seals are shaft-circumference seals and there is a gap at the circumference of the shaft, a substance in the machine where the shaft is mounted sometimes leaks out of the gap when the pressure of the interior of the machine is higher than atmospheric pressure. On the other hand, when pressure of the interior of the machine is less than atmospheric pressure, the air is sometimes introduced into the interior of the machine through the gap. Furthermore gland packings or segment seals are not able to maintain the seal because the contact points to the shaft vary as a result of the axial movement of the shaft.
Though a mechanical seal does not have said problems of gland packings or segment seals, it is unable to permit axial movement of the shaft.